Encapsulated zerovalent iron/nickel-fly ash zeolite foam for treating industrial wastewater contaminated by heavy metals

Abstract

Pollution due to heavy metal discharge into water systems is a global issue that has attracted growing attention in recent years. Thus, we had synthesized encapsulated zerovalent iron/nickel-fly ash zeolite foam (SA-ZFN foam) by freeze-drying method for the simultaneous removal of various heavy metals from industrial wastewater. The resulting SA-ZFN foam’s structural characterization was performed using advanced instrumental techniques. In addition, factors influencing heavy metal removal were discussed including the pH, reaction time, temperature, initial metal concentration, and their competition with each other; and the adsorption mechanism was investigated. The Langmuir maximum capacity of as-prepared foam was 75.76, 49.78, 44.89, and 7.31 mg/g for Cu(II), As(V), Hg(II), and Cr(VI), respectively. Furthermore, isotherms and kinetic data revealed that the rate-limiting step is monolayer adsorption on a homogeneous surface.Furthermore, thermodynamic studies indicated that ΔG° decreases as temperature rises, i.e. the adsorption process becomes more favorable at higher temperatures. The results suggest the no significant decrease of adsorption capacity on each cycle was observed by re-sustaining over three times in the first two cycles. When applied to real industrial wastewater, the SA-ZFN foam reduced the residual heavy metals to acceptable levels. Continuous column experiment also suggested that the SA-ZFN foam could simultaneously remove the heavy metals from aqueous solutions. From these results, it is demonstrated that the SA-ZFN foam is a promising, efficient, and economical material for wastewater treatment.